OBJECTIVES: I. Determine the maximum tolerated dose (MTD) of temozolomide and carboplatin in patients with recurrent glioblastoma multiforme. II. Determine the acute and long-term toxic effects of this regimen in these patients. III. Determine the pharmacokinetics of this regimen in these patients. IV. Determine the potential of either a pharmacokinetic- or pharmacodynamic-mediated drug interaction in patients treated with this regimen. V. Determine the objective response rate in patients treated with the established MTD of this regimen. VI. Determine time to tumor progression and survival in patients treated with this regimen.